Field of the Invention
The invention relates to a hydraulic control device for an emergency stop valve of a steam turbine, The hydraulic control device has a module for the reduction of a hydraulic pressure by rapid opening of an outflow valve and/or unloading or loading an actuator for actuating the emergency stop valve; in an operating medium supply and/or conducting system a control valve arrangement with at least three safety valves is provided, which are hydraulically interconnected in such a manner that these open the outflow valve or unload or load the actuator only when a safety circuit by way of at least two safety valves of the control valve arrangement has assumed an emergency stop position. The invention, furthermore, relates to a steam turbine arrangement.
Steam turbines, for example in power stations, in which live steam from a boiler is expanded and in the process drives one or more turbine stages, must not exceed certain maximum rotational speeds in order to prevent in particular damaging the turbine components. In order to avoid that this maximum rotational speed is exceeded by the turbine during a load dump or a coupling breakage or the like, it is known for example from DE 10 2004 042 891 B3 to provide an emergency stop valve which in as short as possible a time interrupts or reduces the steam mass flow to the turbine when for example the turbine rotational speed exceeds a predetermined threshold value or an impending exceeding of the maximum rotational speed is detected in another way.
Consequently, high availability, safety and reliability requirements are made on such emergency stop valves and their activation. Usually, an emergency stop valve therefore comprises a working cylinder or actuator which is lifted by a hydraulic pressure against a preload element, for example a spring and thus actively opens the emergency stop valve, for as long as the hydraulic pressure overcomes the preload of the preload element. For closing the emergency stop valve, this hydraulic pressure is reduced as quickly as possible, for example discharged in a controlled manner into a tank. The pressureless working cylinder is forced by the preload element into the closed position of the emergency stop valve.
To this end, DE 10 2004 042 891 B3 proposes a control device for an emergency stop valve of a steam turbine with a module for reducing a hydraulic pressure by quickly opening an outflow valve, wherein a control valve arrangement with at least three safety transfer valves is provided, which are hydraulically interconnected in such a manner that these close the emergency stop valve only when at least two safety transfer valves of the control valve arrangement have assumed an emergency stop position. The control device is designed in such a manner that the hydraulic pressure, when a defined event occurs, can be reduced almost immediately. This is described as a so-called 2oo3 connection (two out of three).
By way of a test control valve arrangement a test, in particular a so-called partial stroke test of the emergency stop valve can be carried out in that, starting out from the emergency stop valve which is for example completely opened or opened into a normal operating position, the hydraulic pressure is initially reduced in such a manner that the emergency stop valve closes entirely or at least partially in that for example the working cylinder or actuator performs a full or a partial stroke. Following this the hydraulic pressure is increased again and the emergency stop valve thus moved back into its starting position.
By way of this test, which can be carried out before, during and/or after the working operation of the turbine, the function of the emergency stop valve can be checked independently of the control valve arrangement of the safety valves and thus a sluggishness or seizure, for example through scale deposit, can be detected.
DE 10 2011 082 599 A1 shows a valve arrangement as it can be used for example for turbines. This valve arrangement comprises a 2oo3 logic. To this end, a first, a second and a third precontrol valve are provided, wherein each of these precontrol valves controls two safety valves. Because of this, three connection branches are obtained, wherein the valve arrangement is characterized in that the safety valve is divided into inlet and outlet valves and these are coupled in such a manner that the inlet and outlet valves overlap across connection branches. This means that in each case two of the inlet valves and two of the outlet valves are serially connected to one another in order to jointly form the connection branches. It is provided that three precontrol valves are each assigned two inlet valves and two outlet valves. Here, an arrangement is provided that one of the two inlet valves and one of the two outlet valves are arranged in the first connection branch and the other inlet valve and the other outlet valve are arranged in the further connection branch, but the other outlet valve is fed on the first connection branch.
A precontrol valve according to the prior art is thus assigned to a plurality of inlet and outlet valves even in different connection branches. When a precontrol valve is defective, this accordingly affects two connection branches. A redundant switching technology, such as for example a “2oo3” connection is no longer functional.
If one of the precontrol valves is defective, for example the detection device on the multi control valve, the sensor or the like, the running operation therefore has to be interrupted or at least the so-called TRIP function be waived.
The TRIP function consists in immediately switching off a steam turbine, for example in an emergency. In the process, three safety transfer valves are switched. The triggering is effected via a 2oo3 (two out of three) connection. This means the controlled discharge of the control fluid for tripping is effected by actuating at least two safety transfer valves.
From the publication EP 0433 791 A1 an embodiment with three safety valves in the form of transfer valves with solenoid valves assigned to the safety valves for actuating the same is known. Upon a failure of one of the safety valves, the operation of the safety valve can nevertheless be maintained by closing the actuating valve assigned to the same. Here, the actuation valves only serve as actuation element of the safety valve and have no influence on the inflow to the safety valve, which is why a replacement of a single safety valve during running operation is not possible.